Saikawa et al. in U.S. Pat. No. 4,087,424 disclose penicillin and cephalosporin compounds having a substituted piperazindioncarbonylamino acyl sidechain. Cephalosporins having an (N-alkyl piperazindioncarbonylamino) substituent on the 2-position carbon atom of a phenylacetamido sidechain are specifically disclosed as compounds 60-71.
Bayer in Belgian Pat. No. 836,022 disclose penicillin and cephalosporin compounds having an imino substituted imidazoledioncarbonylamino group at the 2-position carbon atom of a phenylacetamido, cyclohexenylacetamido, or cyclohexadienylacetamido acyl sidechain.